The present invention relates to load power switching circuits and, more particularly, to a novel method of, and apparatus for, controlling a selected one of the average or R.M.S. magnitude of A.C. voltage across a load.
It is known to control the magnitude of a current flowing through a load from an A.C. source by means of a phase-control circuit, utilizing either forward-phase control or reverse-phase control (the latter as described and claimed in my co-pending application Ser. No. 529,296, filed on Sept. 6, 1983, now U.S. Pat. No. 4,528,494 assigned to the assignee of the present application and incorporated herein in its entirety by reference). In many uses, open-loop control of the load voltage magnitude, and therefore of the load power, is adequate. In many other uses, e.g. a line voltage converter for energizing lower voltage incandescent lamps, closed-loop control of the load (lamp) voltage magnitude, and therefore of the load power, is desirable. It is also desirable that any load voltage magnitude control method and apparatus, whether controlling the "average", i.e. mean absolute deviation (MAD), or root-mean-square (RMS) magnitude, be utilizable with any switched-voltage or phase-control (whether forward-control or reverse-control) voltage converter and also be equally as well suited for use with power switching devices, placed in series between the controlled load and an A.C. source, of regenerative or controlled-turn-off types. It is also highly desirable that any load voltage magnitude control apparatus be capable of operating in conjunction with load current control means, such as the reverse-phase load current control means of the aforementioned co-pending application, which provides load control during the high "inrush" current magnitude initial interval when a "cold" load is first energized.